1. Field of the Invention
The present invention relates to an engine starter including an output shaft rotated by motor drive and a clutch provided to the output shaft for transmitting a rotation force applied in one direction of the output shaft to a pinion gear.
2. Description of the Related Art
Conventionally, there is known an engine starter including a driving body of a cylindrical shape having a tapered notch portion at an inner peripheral surface thereof, a rotary shaft defining a wedge-shaped space between the inner peripheral surface of the driving body and itself, and a roller provided in the wedge-shaped space and capable of rolling along a peripheral direction of the rotary shaft, in which, when the driving body rotates in one direction, the roller bites into the driving body on a narrower side of the wedge-shaped space and the rotary shaft, thereby allowing the rotation force of the driving body to be transmitted to the rotary shaft.
The inner peripheral surface of the driving body on the narrower side of the wedge-shaped space is formed with a lock portion extending inwardly in a radius direction. The roller abuts on the lock portion, thereby limiting a biting depth of the roller into the driving body on the narrower side of the wedge-shaped space and the rotary shaft (see, for example, Japanese Utility Model Application Laid-open No. Sho 59-26107)
For example, in such a case where an abnormal impact force is generated between a pinion gear and a ring gear by meshing of the rotating pinion gear and the ring gear with each other when the ring gear of an engine rotates in a reverse direction, the roller bites into the driving body and the rotary shaft, but the biting depth is limited by the lock portion, thereby causing the roller and the rotary shaft to slide with respect to each other, so damage of the ring gear or the like is prevented.
However, in this case, since the roller and the rotary shaft slide with each other, frictional heat is generated on the roller, thereby causing a rolling contact surface of the roller to be tempered. Thus, hardness of the rolling contact surface of the roller decreases.
As a result, the rolling contact surface of the roller coming into contact with the rotary shaft is deformed. Therefore, the biting depth of the roller into the rotary shaft decreases. Thus, there is a problem in that transmission of a rotation force from the driving body to the rotary shaft is reduced.